Semiconductor device formed over a surface with a depression portion and a projection portion

Abstract

A semiconductor device production system using a laser crystallization method is provided which can avoid forming grain boundaries in a channel formation region of a TFT, thereby preventing grain boundaries from lowering the mobility of the TFT greatly, from lowering ON current, and from increasing OFF current. Rectangular or stripe pattern depression and projection portions are formed on an insulating film. A semiconductor film is formed on the insulating film. The semiconductor film is irradiated with continuous wave laser light by running the laser light along the stripe pattern depression and projection portions of the insulating film or along the major or minor axis direction of the rectangle. Although continuous wave laser light is most preferred among laser light, it is also possible to use pulse oscillation laser light in irradiating the semiconductor film.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a semiconductor device constructed by a semiconductor film that has a crystal structure, and more specifically, to a semiconductor device using a thin film transistor whose active layer is formed of a crystalline semiconductor film obtained through crystal growth on an insulating surface. The present invention also relates to a semiconductor device product ion system using laser light.2. Description of the Related ArtIn recent years, techniques for forming TFTs on a substrate have made great advancements and applications of TFTs to active matrix type semiconductor display devices are being developed. In particular, TFTs formed of polycrystalline semiconductor films (hereinafter referred to as polysilicon TFT) have higher field effect mobility (also referred to as mobility) than conventional TFTs that use amorphous semiconductor films, and accordingly can operate at high speed. Therefore pixels can b...

AI Technical Summary

Benefits of technology

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is therefore to provide a semiconductor device production system using a laser crystallization method which can avoid forming grain boundaries in a channel formation region of a TFT, thereby preventing grain boundaries from lowering the mobility of the TFT greatly, from lowering ON current, and from increasing OFF current.

After the semiconductor film is formed, the semiconductor film may be crystallized by laser light irradiation without exposing the film to the air (for example, noble gas, nitrogen, oxygen, or other specific gas atmosphere or a reduced pressure atmosphere is employed). This structure can prevent molecule-level contaminants in a clean room, such as boron contained in a filter for enhancing the cleanliness of the air, from mixing in the semiconductor film during laser light crystallization.

Problems solved by technology

Glass substrates have poor heat-resistance and are easily deformed by heat.

As a result, continuous wave lasers are now suddenly attracting attention.

These crystal grains have varying sizes and are positioned at random, and it is difficult to specify the position and size of crystal grains in forming a crystalline semiconductor film.

Therefore, grain boundaries in an active layer, in particular, in a channel formation region of a TFT, seriously affect TFT characteristics by lowering the mobility of the TFT greatly, by lowering ON current, and by increasing OFF current since a current flows in grain boundaries.

However, prior art is mostly unsuccessful in forming a crystalline silicon film with no grain boundaries by laser annealing.

Therefore no TFT whose active layer is formed of a crystalline silicon film crystallized by laser annealing has succeeded in obtaining characteristics that rival the characteristics of a MOS transistor manufactured on a single crystal silicon substrate.

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